The present invention relates to a tunneling magnetoresistive element, and also to a magnetic head and memory device utilizing the tunneling magnetoresistive element. The present invention relates also to a method of manufacturing these devices.
As an example of the magnetic sensor based on: tunneling magnetoresistance effect (TMR), a TMR element is proposed by S. Jagadeesh Moodera and Lisa R. Kinder (J. Appli. Phys. Vol.79 (1996), No. 8, pp.4724) (Publication 1); and by J. C. Slonczewski (Physical Review B Vol.39 (1989), No. 10, pp.6995) (Publication 2). Since this TMR element is capable of exhibiting a large magnetoresistance effect as compared with the conventional magnetoresistive element (MR element), the application thereof as a read magnetic head is highly expected.
This TMR element is constructed as shown in FIG. 1 such that a tunnel barrier layer 300 is sandwiched between a first magnetic layer 200 and a second magnetic layer 100. In this case, the first magnetic layer 200 is formed on the surface of a lead wire layer 400 formed on a substrate 500 and is connected with an external electric circuit. On the other hand, the second magnetic layer 100 is also connected with the external electric circuit. If, in the case, these two kinds of magnetic layers 100 and 200 differ in coercivity from each other, there will be generated a phenomenon that, the orientation of the magnetization of these magnetic layers 100 and 200 becomes parallel or anti-parallel with each other corresponding to the changes in external magnetic field 800.
Meanwhile, when a bias voltage V is applied between these two kinds of magnetic layers 100 and 200, a tunnel current I is allowed to flow therebetween through the tunnel barrier layer 300 with the tunnel resistance R in this case being defined by R=V/I. It will be recognized through the observation of the magnitude of the tunnel resistance R whether the orientation of the magnetization of the two magnetic layers 100 and 200 is parallel or anti-parallel. A device which is capable of outputting the changes of tunnel resistance R of a TMR element corresponding to the change of the external magnetic field 800 is the aforementioned magnetic sensor based on tunneling magnetoresistance effect.
As disclosed in the aforementioned publication No. 1, the magnitude of changes of tunnel resistance R is mainly determined by the value of the polarizability P1 of a magneticllayer 100 and also by the value of the polarizability P2 of a magnetic layer 200. The value of xe2x80x9cpolarizabilityxe2x80x9d is closely related to the magnitude of magnetization (=spin polarizability) of a substance, and the magnitude of magnetization is a value which is specific to a substance. As the magnitude of xe2x80x9cpolarizabilityxe2x80x9d becomes closer to 1, the magnitude of changes of tunnel resistance R would become larger.
For each magnetic layer, the value of xe2x80x9cpolariziabilityxe2x80x9d can be determined by finding the number of electronic state which is capable of contributing to the tunnel conduction. Namely, the xe2x80x9cpolarizabilityxe2x80x9d inside each magnetic layer is determined by a difference between the number of spin-up state and the number of spin-down state, both of which are capable of contributing to the tunnel conduction. A difference in number between the number of spin-up state and the number of spin-down state also becomes an issue on the occasion of determining the magnetization of a metallic magnetic body. The numbers of electronic state to be employed for defining the value of xe2x80x9cpolarizabilityxe2x80x9d here differs from that to be employed for determining the ordinary magnetization in the respect that only the electronic states which are capable of contributing to the tunnel conduction is taken up out of the possible electronic states inside the magnetic layers. In other words, when only the electron which is capable of contributing to the tunnel conduction is taken into consideration, the value of xe2x80x9cpolarizabilityxe2x80x9d discussed herein is not necessarily identical with the value of ordinary magnetization.
An object of the present invention is to provide a tunneling magnetoresistive element which is capable of obtaining a higher xe2x80x9cpolarizabilityxe2x80x9d and hence capable of achieving a larger magnitude of changes in tunnel resistance R, which can be realized by optimizing the selection of electronic states that can contribute to the tunnel conduction even though a magnetic material having the same magnetization is employed.
Another object of the present invention is to provide a high sensitivity magnetic head and the method of manufacturing such a magnetic head.
A further object of the present invention is to provide a magnetic memory which is non-volatile and is capable of reading and writing data at a high speed, and the method of manufacturing such a magnetic memory.
First of all, the meaning of the state called xe2x80x9can electronic state that can contribute to the tunnel conductionxe2x80x9d will be explained. This electronic state may be summarized in such a way that it is (1) an electronic state in the vicinity of Fermi surface and at the same time, (2) an electronic state having a wavevector which is perpendicular to tunnel junction plane (i.e. parallel with the direction of thickness of tunnel barrier). When these electronic states of the magnetic material are located in the wavevector space, the aforementioned electronic states that can contribute to the tunnel conduction are specified by the wavevectors which are roughly normal to the tunnel junction plane and which have the lengths that roughly correspond to the length of the Fermi energy of the direction.
The aforementioned requirement (2) are brought about by the wavevector selectivity of the tunnel barrier. As reported by E. Wolf, in xe2x80x9cPrinciples of Electron Tunneling Spectroscopyxe2x80x9d Oxford University Press, Oxford, 1989, pp. 23 (Publication 3), in the case of ideal dielectric tunnel barrier which is constituted by infinite planes and where alumina, etc. is employed, the transmission factor of tunneling electron becomes maximum when the wavevector of tunneling electron that can be described by a plane wave is parallel with the normal line of tunnel barrier. However, when the wavevector begins to include a component perpendicular to the normal line of the tunnel barrier, the transmission factor of tunneling electron will be sharply decreased. When it is assumed that the barrier height is 2 eV, the thickness of tunnel barrier is 1 nm, and Fermi level is 5 eV, the angle between the direction of normal line and the wavevector as the transmission factor of tunneling electron falls down to 1/e (e: the base of natural logarithm) would become only around 8 degrees. Namely, the wavevector of the tunneled electron is very well aligned. It may be said in view of this fact that the tunnel barrier where the flatness thereof is sufficiently ensured is a device exhibiting a highlyefficient wavevector selectivity. In other words, the electronic state of the electron that has been taken up by the tunneling from the magnetic layer can be said to be only the electronic states included in a region of a very small solid angle which spreads around the gamma (xcex93) point in the wavevector space.
Therefore, it is very likely that the tunneling electron to be obtained from a group of electronic states where the direction of wavevector is very sharply aligned is characteristically very sensitive to the anisotropy of the Fermi surface, i.e. the crystal anisotropy.
Such a characteristic of the tunneling electron can be inferred also from the experiment of magnetic Compto scattering where circular polarized X-ray is employed as set forth by Yoshidazu Tanaka, Nobuhiko Sakai, Yasunori Kubo and Hiroshi Kawata in xe2x80x9cPhysical Review Lettersxe2x80x9d, Vol. 70, No.10, 1993, pp.1537-1540 (Publication 4). In this experiment, the polarizability of electron taken up from the surface of iron by means of circular polarized X-ray is directly measured, obtaining the result that the polarizability of electron to be released in the xcex93-N direction is larger than the value of polarizability of electron to be released in the xcex93-H direction.
As explained above, the present invention makes use of the fact that the polarizability of magnetic crystal exhibits a prominent anisotropy. Namely, by taking advantage of the wavevector selectivity of the tunnel barrier, the orientation of crystal face which exhibits a larger variation of tunnel magnetoresistance was investigated by the present inventors. As a result, it was found that the orientation exhibiting a large polarizability was (211) plane (crystal face, the same hereinafter) and (110) plane in the cases of iron and iron alloys.
FIG. 2 is a cross-sectional view schematically illustrating one example of the structure of a TMR device according to the present invention which enables to increase the magnitude of changes of tunneling magnetoresistance. As shown in FIG. 2, the TMR device is constituted by a first magnetic layer 210, a tunnel barrier layer 310 and a second magnetic layer 110. The first magnetic layer 210 is formed on the surface of a buffer layer 250 comprising at least one layer and is constituted by a thin crystal film which has been grown according to a specific crystal orientation that is determined by the kind and crystal orientation of the material of the buffer layer 250. Therefore, the specific crystal face of the first magnetic layer 210 appears at a junction plane between the tunnel barrier layer 310 and the first magnetic layer 210.
In this case, due to the wavevector selectivity of the tunnel barrier, only the electron exhibiting an electronic state having a wavevector which is perpendicular to the aforementioned junction plane is allowed to selectively tunnel from the first magnetic layer 210 to the second magnetic layer 110. This electronic state concurrently constitutes an electronic state having a wavevector which is perpendicular to the crystal face appearing on the junction plane of the first magnetic layer 210. Namely, by determining which crystal face should be selected for the junction plane of the first magnetic layer 210, only the electron of the electronic state of a specific kind will be selected among the electronic states represented by the wavevector within the wavevector space of a crystal material constituting the first magnetic layer 210.
The aforementioned crystal orientation differs depending on the material constituting the first magnetic layer 210; Any magnetic material can be employed as the first magnetic layer 210 provided that the orientation for optimizing the polarizability of a magnetic material is known and that the growth direction of the material can be so chosen to realize the optimum. The iron is only a pure ferromagnetic material exhibiting a bcc structure. On the other hand, iron alloys such as an iron-cobalt alloy, an iron-nickel alloy, an iron-chromium alloy, an ironrhodium alloy, an iron-platinum alloy, an iron-palladium alloy, an iron-iridium alloy and an iron-vanadium alloy also have the bcc structure and are ferromagnetic. Therefore, these materials are useful in the present invention.
In the process of accomplishing the present invention, various kinds of TMR elements were manufactured, each using the magnetic layer 210 having a different crystal orientation by making use of the aforementioned magnetic materials and then, changes of tunnel magnetoresistance were observed to search the orientation which is capable of optimizing the polarizability. As a result, it was found that the TMR element where (211) plane was employed was capable of exhibiting the largest changes in tunnel magnetoresistance. It was found that the TMR element which was capable of exhibiting next largest changes in tunnel magnetoresistance was one where (110) plane was employed. The magnitude of the changes in the latter TMR element was about 80% of the former TMR element where (211) plane was employed. In the cases of the TMR elements where other crystal faces were employed, the magnitude of the changes was not higher than 25% of the TMR element where (211) plane was employed. It was found from these results that most effective crystal orientation was (211) plane, and that, the (110) plane was also effective though it was inferior more or less as compared with the (211) plane.
The crystal orientation of the buffer layer 250 is determined depending on the crystal orientation of a lead wire layer 410 disposed underneath the buffer layer 250, and the crystal orientation of the lead wire layer 410 is determined depending on the kind of material and crystal orientation of a substrate 510 disposed underneath the lead wire layer 410. In other words, the factor which controls the crystal orientation of the magnetic layer 210 is the combination of the kinds and crystal orientations of the buffer layer 250, the lead wire layer 410 and the substrate 510.
By the way, in order to enable the tunnel barrier 310 to become a powerful wavevector selector, the junction plane between the magnetic layer 210 and the magnetic layer 110 is required to have a very high degree of flatness. For the purpose of obtaining this high degree of flatness, the tunnel barrier layer 310 of the present invention was formed by way of a method called xe2x80x9ctwo-stage oxidation methodxe2x80x9d.
As shown in the prior art such as the aforementioned Publication 1 and Applied Physics Letters, Vol. 71, No.22, 1997, pp.3296-3298 (Publication 5); H. Tsuge and T. Mitsuzuka, an aluminum oxide film has been employed for manufacturing a tunnel barrier of relatively high reliability. In the present invention also, an aluminum oxide film is employed for manufacturing a tunnel barrier. However, the method of forming a tunnel barrier according to the present invention, differs from the conventional method. Aluminum is known to be excellent in wettability to the surface of main magnetic metals such as iron, cobalt, nickel and alloys thereof. FIGS. 3 to 6 illustrate examples of manner of forming an aluminum oxide film (alumina) on the surface of the (001) plane of magnetic layer 211 wherein iron (Fe) was employed for constituting the magnetic layer 211. For convenience sake, the same components are referred to by the same reference numerals in these FIGS. 3 to 6.
FIG. 3A shows a state obtained when an aluminum thin film 320 was formed so that a thickness of the film was lnm or less by way of vapor deposition on the magnetic layer 211 ((001) plane of iron) by making use of an ultra-high vacuum device. When the thickness of aluminum is sufficiently thin (1 nm or less), aluminum is enabled to densely cover the (001) Fe plane owing to a high wettability of aluminum, and at the same time, an aluminum thin film 320 having the (001) plane is allowed to grow reflecting the crystal face of the Fe. This fact was confirmed by the observation of RHEED (Reflective High Energy Electron Diffraction) pattern, and at the same time, the formation of an extremely flat interface between the aluminum thin film 320 and the Fe (001) plane was also confirmed. Subsequently, when oxygen gas was introduced into the ultra-high vacuum device, the aforementioned RHEED pattern was turned into a pattern indicating the formation of amorphous layer. This implied that, as shown in FIG. 3B, an aluminum oxide layer 330 having a very high flatness was formed, thus indicating an excellent interface formed between the tunnel barrier layer and the (001) Fe plane. By the way, upon the oxidation of aluminum, the original aluminum layer with a thickness of 1 nm was transformed into the aluminum oxide layer 330 with a thickness of 1.3 nm.
On the other hand, as shown in FIG. 4A, when aluminum is deposited to an increased thickness (more than 1 nm), not only the (100) plane of aluminum, but also (111) plane thereof was caused to generate (or a phenomenon of so-called facetting), thereby generating a slightly projected and recessed pattern on the surface of the aluminum layer 321. This fact was confirmed by a change of RHEED pattern. Even if oxygen gas was introduced into the ultra-high vacuum device, the aforementioned RHEED pattern was not turned into a pattern indicating the formation of complete amorphous state, thereby leaving the projected and recessed pattern as it was. As a result, a structure wherein the residual aluminum portions were enveloped was formed as shown in FIG. 4B, thus producing an aluminum oxide layer 331 having a projected and recessed surface. Under this condition, not only the wavevector of (001) orientation, but also the wavevector of (111) orientation may possibly be allowed to tunnel, thereby weakening the selectivity of wavevector. Therefore, it is difficult to manufacture a tunnel barrier having a thickness of 1.3 nm or more and yet exhibiting a sufficient flatness if the manufacture of the tunnel barrier is to be performed by simply oxidizing an aluminum film.
The demand to form a tunnel barrier having a thickness of 1.3 nm or more cannot be disregarded from the viewpoint of controlling the characteristics of TMR element. Under the circumstances, a method shown in FIG. 5 was tried. FIGS. 5A and 5B show a process wherein an aluminum oxide layer 330 having a thickness of 1.3 nm or less was formed by a method shown in FIG. 3. Then, the ultra-high vacuum device was exhausted again so as to purge the oxygen that had been introduced into the vacuum device for the purpose of oxidizing aluminum. Thereafter, aluminum was vapor-deposited to a thickness of 1 nm to thereby form an aluminum layer 322 as schematically shown in FIG. 5C. Although there was no possibility that the facetting shown in FIG. 4 would be produced, since the wettability of aluminum to the surface of alumina was insufficient, aluminum grains were caused to generate, thus forming an aluminum film 322 which was rather closer to a polycrystalline thin film. Thereafter, oxygen was introduced into the vacuum device to thereby form an aluminum oxide layer 322 through the oxidation of the aluminum film 322. However, a varied degree of oxidation was admitted along the grain boundary. Namely, it was found through the measurement employing STM/AFM that there were pin-holes originating from the grain boundary or the non-uniformity of tunnel barrier height, thereby making it impossible to obtain an excellent tunnel barrier property.
Under the circumstances, in the present invention, the xe2x80x9ctwo-stage oxidation methodxe2x80x9d as shown in FIG. 6 has been developed. FIGS. 6A and 6B show a process wherein an aluminum oxide layer 330 having a thickness of 1.3 nm or less was formed in the same manner as shown in FIG. 3. Then, as shown in FIG. 6C, aluminum was vapor-deposited without performing the purging of the ultra-high vacuum device and with a constant partial pressure of oxygen being maintained therein. As a result, an aluminum oxide layer 333 was formed directly from the aluminum flux as shown in FIG. 6C. According to this method wherein the aluminum oxide layer 333 is deposited on the same material, i.e. the aluminum oxide layer 330, the generation of crystal grain boundary originating from the insufficiency of wettability can be suppressed, thereby making it possible to obtain a tunnel barrier layer which is very homogenous and excellent in surface flatness. According to this method, excellent tunnel barrier properties were observed in the tunnel barrier layers having a film thickness ranging from 1 nm to 3 nm with the excellent homogeneity and flatness thereof being maintained. According to this method, there is no limitation in principle with respect to the upper limit of film thickness.
It should be noted that when the processes of FIGS. 6A and 6B are omitted, it is impossible to obtain an excellent tunnel barrier layer, even if the formation of aluminum oxide layer is performed as shown in FIG. 6C by exposing the (001) Fe plane of the surface of the magnetic layer 211 to an oxygen atmosphere. Because, since aluminum oxide is poor in wettability to the (001) Fe plane, grains would be generated in the aluminum oxide layer. Therefore, it is imperative to form in advance a thin (not more than 1.3 nm in thickness) aluminum oxide layer 330 as shown in FIG. 6B.
As explained with reference to FIG. 3, as long as the film thickness of aluminum is confined to not more than 1 nm, it is always possible to form an excellent aluminum oxide layer 330 on almost all kinds of magnetic layer, i.e. irrespective of the kind of material and the orientation of crystal face. Therefore, the method employing the aforementioned two-stage oxidation is optimum and indispensable for the tunnel barrier-forming method of the present invention wherein electrons having a specific wavevector are taken up from any optional material.
For example, in the method shown in FIG. 4, if a surface which is capable of lattice-matching with the (111) plane of aluminum is employed as the surface of the magnetic layer 211, the (111) plane of aluminum will be formed from the beginning instead of forming the (001) plane thereof. In this case, the facetting would not be generated and hence a flat tunnel barrier can be obtained. However, since the crystal orientation or materials of the magnetic layer 211 are limited and it is impossible to optionally select other orientations, this method is not useful in the present invention. In other words, the aforementioned two-stage oxidation method is indispensable for realizing the method of the present invention wherein tunneling electrons having a specific wavevector are taken up by taking advantage of the selectivity of wavevector.
In the aforementioned two-stage oxidation method, the oxidation of aluminum was performed through the natural oxidation thereof by the oxygen that had been introduced into an ultra-high vacuum device. However, it was also possible to form a tunnel barrier layer having a high barrier height by performing the oxidation of aluminum in an atmosphere containing UV ozone or oxygen radicals generated from oxygen plasma. It was possible according to this method to increase the changes of tunneling magnetoresistance to twice as high as that to be derived from the natural oxidation.
The aforementioned two-stage oxidation method may be said to be a method for ensuring the flatness, and also a method for enabling a very thin film of dielectric tunnel barrier to be formed by eliminating the projection and recess of atomic size level from the surface of layer. In this respect, the two-stage oxidation method is especially effective when the value of tunnel resistance of TMR element is desired to be minimized. Further, the two-stage oxidation method is also useful as a method of precisely controlling the value of tunnel resistance in the range of eight figures.
In summary, this xe2x80x9ctwo-stage oxidation methodxe2x80x9d, can be defined as being a method of forming an aluminum oxide thin film, the method comprising a first stage wherein an aluminum film having a thickness of 1 nm or less is formed on the surface of a magnetic metal by taking advantage of the excellent wettability of aluminum to the surface of main metals, the resultant aluminum oxide film formed by subsequent natural oxidization of the aluminum or oxidization of the alminum by oxygen radical; and a second stage wherein an aluminum oxide thin film is deposited directly from an aluminum flux in an oxygen atmosphere or an atmosphere of oxygen radical.
As explained above, the tunneling magnetoresistive element according to the present invention comprises a multi-layer film composed of a first magnetic layer, a tunnel barrier layer, and a second magnetic layer, which are successively deposited in the mentioned order, wherein said first magnetic layer is formed of a ferromagnetic material having a bcc structure, and a junction plane between said first magnetic layer and said tunnel barrier layer is constituted by (211) plane or (110) plane of said first magnetic layer.
As for the ferromagnetic material having a bcc structure, it is possible to employ an iron-cobalt alloy, an iron-nickel alloy, an iron-chromium alloy, an iron-rhodium alloy, an iron-platinum alloy, an iron-palladium alloy, an iron-iridium alloy and an iron-vanadium alloy. Further, the second magnetic layer can be constituted by iron, nickel, cobalt or alloys thereof.
Alternatively, a tunneling magnetoresistive element according to the present invention comprises a multi-layer film composed of a buffer layer, a first magnetic layer, a tunnel barrier layer, and a second magnetic layer, which are successively deposited in the mentioned order on the surface of a substrate, and is characterized in that the first magnetic layer is formed of a ferromagnetic material having a bcc structure, and that a junction plane between the first magnetic layer and the tunnel barrier layer is constituted by (211) plane or (110) plane of the first magnetic layer.
In the case where the junction plane between the first magnetic layer and the tunnel barrier layer is constituted by (211) plane of the first magnetic layer, it is preferable that the buffer layer is constituted by a layer having A-plane of cobalt or a cobalt-chromium alloy each having an hcp structure, (211) plane of chromium having a bcc structure, (110) plane of gold having a fcc structure, (110) plane of magnesium oxide, (11-20) plane of sapphire or (001) plane of a titanium-chromium alloy having a bcc structure; or constituted by a multi-layer structure formed of a combination of two or more layers having two or more said planes.
In the case where the first magnetic layer is formed of single crystal, and the junction plane between the first magnetic layer and the tunnel barrier layer is constituted by (110) plane, it is preferable that the buffer layer is constituted by a layer having (110) plane of molybdenum having a bcc structure, (110) plane of tungsten having a bcc structure, (110) plane of tantalum having a bcc structure or (110) plane of chromium having a bcc structure; or constituted by a multi-layer structure formed of a combination of two or more layers having two or more said planes.
In the case where the first magnetic layer is formed of polycrystal, and the junction plane between the first magnetic layer and the tunnel barrier layer is constituted by (110) plane, it is preferable that the buffer layer is constituted by a layer having (111) plane of a metal having a fcc structure or (0001) plane of a metal having an hcp structure; or constituted by a multi-layer structure formed of a combination of two or more layers having two or more said planes.
The junction plane between the first magnetic layer and the tunnel barrier layer may be a crystal face having an inclined angle of not more than 10 degrees as measured from the (211) or (110) plane of the first magnetic layer.
Alternatively, a tunneling magnetoresistive element according to the present invention may be constructed such that the substrate is formed of a semiconductor substrate, and that said element comprises a multi-layer film wherein an amorphous thin film layer formed of at least one kind of film selected from the group consisting of silicon oxide film, aluminum oxide film and other metal oxide films is interposed between the buffer layer and the semiconductor substrate.
As explained in the paragraph of prior art, the existence of difference in coercivity between the first magn etic layer and the second magnetic layer is indispensable for the development of the tunneling magnetoresistive effect. Therefore, unless the coercivity of each magnetic layer is independently controlled so as to realize a required magnitude of coercivity in each magnetic layer, it would be impossible to obtain an effective tunneling magnetoresistive element. A required magnitude of difference in coercivity is ordinarily realized by suitably selecting the material of magnetic layers. However, if it is impossible to obtain an effective difference in coercivity through the selection of the material of each magnetic layer, the following method can be adopted.
Namely, if it is desired to provide the first magnetic layer with a higher coercivity, a magnetic layer having a higher coercivity than that of the first magnetic layer should be employed as a buffer layer. On the other hand, if it is desired to provide the second magnetic layer with a higher coercivity, a ferromagnetic layer or an anti-ferromagnetic layer having a higher coercivity than that of the second magnetic layer should be deposited on the second magnetic layer (Namely, on the surface of the second magnetic layer disposed opposite to the tunnel barrier layer).
The tunneling magnetoresistive element according to the present invention is suited for use in a magnetic head. Further, the tunneling magnetoresistive element according to the present invention is suited for use as an element of a magnetic memory comprising a plurality of tunneling magnetoresistive elements which are arrayed in a matrix pattern, means for selectively applying a magnetic field onto each tunneling magnetoresistive element, and means for selectively detecting the resistance of each tunneling magnetoresistive element.
According to the present invention, there is also provided a method of manufacturing a magnetic head comprising a multi-layer film composed of a first magnetic layer, a tunnel barrier layer, and a second magnetic layer, which are successively deposited in the mentioned order, the method being characterized in that a ferromagnetic material having a bcc structure is employed as the first magnetic layer, that an aluminum film having a thickness of 1 nm or less is formed on the (211) plane or (110) plane of the first magnetic layer, that the aluminum film is naturally oxidized or oxidized by oxygen radical to form an aluminum oxide film, and that an aluminum oxide film is formed on the first-mentioned aluminum oxide film directly from aluminum flux in an oxygen atmosphere or an atmosphere of oxygen radical to thereby form the tunnel barrier layer.
According to the present invention, there is also provided a method of manufacturing a magnetic memory comprising a plurality of tunneling magnetoresistive elements each comprising a multi-layer film composed of a first magnetic layer, a tunnel barrier layer, and a second magnetic layer, which are laminated in the mentioned order; means for selectively impressing a magnetic field onto each tunneling magnetoresistive element; and means for selectively detecting the resistance of each tunneling magnetoresistive element; the method being characterized in that a ferromagnetic material having a bcc structure is employed as the first magnetic layer, that an aluminum film having a thickness of 1 nm or less is formed on the (211) plane or (110) plane of the first magnetic layer, that the aluminum film is naturally oxidized or oxidized by oxygen radical to form an aluminum oxide film, and that an aluminum oxide film is formed directly from an aluminum flux on the first-mentioned aluminum oxide film in an oxygen atmosphere or an atmosphere of oxygen radical to thereby form the tunnel barrier layer.